1. Field of the Invention
The invention pertains to the field of horticulture. More particularly, the invention pertains to plant growing media.
2. Description of Related Art
Growing media used in container production in greenhouses or plant nurseries mostly include peat moss, also known as moss peat or sphagnum peat, and barks, which may include both hardwood barks and softwood barks. Some media use only peat with a small amount of perlite or vermiculite. Perlite is a siliceous mineral of volcanic origin. It is produced by heating igneous rock under industrial high temperatures (1,100 to 1,600° F.) until a light powdery substance results. Lightness and uniformity make perlite very useful for increasing the aeration and drainage in a growing medium. However, perlite is dusty and has a tendency to “float” upwards in container media. It is often included in the mix solely to improve the drainage. Vermiculite is a micaceous mineral made by heating in a kiln at temperatures up to 745° C. The result is an expanded, plate-like particle with a high water-holding and mineral-holding capacity that aids in aeration, drainage, and nutrient retention in growing media. Vermiculite is considered less durable than sand or perlite, but its properties are considered generally desirable for container media. However, vermiculite has received environmental attention with regard to potential contamination with asbestos-related fibers from a related mica mineral called tremolite. Most producers monitor this issue closely to avoid problems later, and for this reason the use of vermiculite is less desirable. Other porosity agents include mostly pine bark with a small amount of peat.
Peat is the most common component in both nursery and greenhouse mixes but is increasingly in short supply as world resources of this mined product are diminishing. Much of Europe already has mandatory standards for mixes with reduced peat amounts. Peat is usually included in a growing medium mix to increase the water-holding capacity or to decrease the weight of the mix, but peat is very acidic and normally requires up to 5 to 15 pounds of limestone per cubic yard of peat mix to offset the low pH.
These conventional growing media are widely employed for small container ornamental plants, but even with augmentation of the medium with limestone, the pH of the medium may drift quite significantly over time, typically in the direction of more acidic levels. The reasons for this are believed to be the effect of the plants growing in the medium that causes among other things the uptake and loss of nutrients that help buffer pH, acidification of the medium as a result of root transpiration of organic acids, and nitrification of added chemical-ammoniated fertilizer, which causes the release of 2 moles of hydrogen for each mole of nitrogen transformed.
An additional and significant problem with peat moss is the inhibition of moisture uptake or what is called “wetting up”. Water-repellant films on surfaces of the peat inherently tend to make the peat extremely hydrophobic, but if these films can be overcome, the peat itself is capable of absorbing and holding large quantities of water. Most commercial suppliers offer a product with a wetting agent, such as a surfactant, already included if it is intended for use in greenhouses and plant nurseries. If not, users are warned to perform some sort of test to see how difficult it is to wet the product before using the peat moss. If water runs off the product, then the user is instructed to purchase an agent or, if none are available at a reasonable cost, to use hot water to speed-up the wetting process. These factors dramatically increase the inconvenience and cost of using growing media containing peat moss.
The pH change of growing media may indirectly and significantly affect the quality of growth by altering color performance of pH sensitive ornamental plants and generally significantly reducing yield and quality appearance. This is very costly to the ornamental plant industry. Moreover, in the last 20 years, the move away from using soil in greenhouse and nursery container media has resulted in less buffering resistance to pH change, which has indirectly exacerbated the problem. It is not unusual that in peat and bark growing media, a decrease of up to one pH unit in a week, which is a 10-fold increase in acidity, can sometimes occur in commercial crops.
Most plants prefer to grow in relatively a relatively neutral, stable pH growth medium, and the problem of pH drift also affects other areas of horticulture. Ammonium fertilizers, which lower the pH of the soil, are commonly used in agricultural fields, and farmers typically apply lime to counteract the pH effect of the fertilizers. Lime is inexpensive but heavy, making it difficult to transport and difficult for farmers to spread. Lawn care, gardening, and golf course management are other areas where pH drift in the direction of more acidic levels can be highly detrimental to plant growth. The pH drift in the growing medium may be a result of added soil treatments, plant growth itself, acid rain, or other environmental factors.
One reason that so many plants do not survive after purchase is that the chemical controls used by the industry in the growing media leading up to the sale are temporary by nature, as they contain insufficient buffering to extend out weeks, are improperly conceived in that they only partially deal with the pH drift problem, and are reductionist in nature in that additives, typically chemicals, are used to correct a purely natural problem.
Most of the commercial container industry is trapped in this costly and highly environmentally unfriendly struggle to protect against pH and nutrient drift of container media long enough to get the plants safely to market. Additionally, many plants die or are damaged after purchase and use in landscaping by consumers, since the chemical controls employed by professionals at the place of sale are no longer operative or practicable at the home level.
Liability for improperly handled and prepared container media plants extends beyond the point of sale, as surveys show most plant nurseries offer up to a one-year replacement warranties to attract consumers and to stay in the market. This is very costly to the industry, since about 20% of buyers request replanting or restocking of pH-drifted and nutrient-damaged plants that do not satisfactorily survive the warranty period.